This invention relates to chip-type semiconductor light-emitting devices and, more particularly, to a chip-type semiconductor light-emitting device improved in brightness at a center of the radiation surface by the reflector.
Conventionally, there have been known a variety of chip-type semiconductor light-emitting devices using light-emitting diode (LED) elements as light-emitting sources. FIG. 11 and FIG. 12 show one example of such devices. FIG. 11 is a plan view showing a state that an LED element is mounted on a substrate. In FIG. 11, a pair of electrodes 3 and 4 are formed of a conductive material on a surface of the substrate 2.
The substrate 2 is formed, at opposite ends, with semicircular cutouts 2a and 2b on which conductive films, such as plating layers, are formed extending to a backside of the substrate 2 and electrically connected to the pair of electrodes 3 and 4 formed on the surface of the substrate 2. A rectangular pad 3a is formed in one electrode 3 so that an LED element 1 is mounted by die-bonding on the pad 3a. The LED element 1 is electrically connected to the other electrode 4 through wire bonding of a metal wire 5.
An opaque-resin reflector is provided on the substrate 2 mounted with the LED element 1. A translucent resin is filled into an aperture formed in the reflector, thereby forming a chip-type semiconductor light-emitting device. FIG. 12 is a sectional view showing, on a XIIxe2x80x94XII section in FIG. 11, a chip-type semiconductor light-emitting device formed as above.
In FIG. 12, 6 is an opaque-resin reflector having a slant surface 6X that is inclined at an acute angle xcex81 relative to the substrate 2. An aperture 6a is formed encompassed by the slant surface 6X and opening to an outside. The reflector 6 is formed by injection-molding, for example, a white liquid-crystal polymer.
The reflector 6 is rested on the substrate 2 and then an LED element 1 is mounted in the aperture 6a encompassed by the slant surface 6X and penetrating vertically through thereof. Next, a translucent resin 7, such as an epoxy resin, is filled to encapsulate the LED element 1 and metal wire 5 thus forming a chip-type semiconductor light-emitting device 20. The chip-type semiconductor light-emitting device 20 is to be surface-mounted on a printed-circuit board. Electrical connection is to be made between the conductive films formed in the backside of the substrate 2 through the semicircular cutouts 2a and 2b and a circuit pattern on the printed-circuit board.
By forming the slant surface 6X in the reflector 6, the output light of the LED element 1 is reflected upon the slant surface 6X and radiated toward the front of the chip-type semiconductor light-emitting device 20. Due to this, light emission efficiency is improved in the chip-type semiconductor light-emitting device.
In this example, the aperture 6a of the reflector 6 is formed rectangular as viewed from the above.
FIG. 13 and FIG. 14 show another conventional example of a chip-type semiconductor light-emitting device. FIG. 13 is a schematic perspective view showing, by partial projection. FIG. 14 is a sectional view showing a XIVxe2x80x94XIV section in FIG. 13. The same parts as or corresponding elements to those of FIG. 11 and FIG. 12 are denoted by the same difference numerals. In the FIG. 13 example, cutouts are formed in an elongate-hole form at opposite ends of the substrate 2. The elongate-hole cutouts are formed with conductive films, such as plating layers, extending to the backside of the substrate. The pair of electrodes 3 and 4 are respectively connected to the conductive films.
Inside the reflector 6, a slant surface 6Y is provided inclining at an acute angle xcex8 relative to the substrate 2, to thereby form an inverted-conical aperture 6b that is encompassed by the slant surface 6Y and vertically penetrating through the reflector. In the chip-type semiconductor light-emitting device 30 shown in FIG. 13 and FIG. 14, the output light of the LED element 1 is reflected upon the slant surface 6Y toward the front, improving light emission efficiency. Also, in the example of FIG. 13, the aperture 6b of the reflector 6 is formed circular as viewed from the above.
In this manner, the conventional chip-type semiconductor light-emitting device has a reflector having a slant surface vertically penetrating through the reflector so that the output light of the LED element is reflected by the reflector, thereby improving light emission efficiency.
However, in the conventional chip-type semiconductor light-emitting device, because the angle of the reflector slant surface is set at a constant angle, there is a problem that the output-light center brightness cannot be taken high.
Also, the reflector separately manufactured by injection-molding is attached to the substrate mounted with an LED element. Consequently, where there occurs positional deviation in die-bonding an LED onto the substrate, the LED element and the reflector are impossible to realign with each other, resulting in a problem with center-brightness change.
Therefore, it is a primary object of the present invention to provide a novel chip-type semiconductor light-emitting device.
Another object of the invention is to provide a chip-type semiconductor light-emitting device capable of improving radiation center brightness.
Another object of the invention is to provide a chip-type semiconductor light-emitting device capable of reducing change or variation in center brightness even if there is positional deviation of the LED element relative to the substrate.
A chip-type semiconductor light-emitting device according to the present invention comprises: a substrate; a semiconductor light-emitting element mounted on the substrate; and a reflector having an aperture having a slant surface in an inner wall thereof and to be rested on the substrate in a manner encompassing the semiconductor light emitting element by the slant surface, the slant surface including first and second reflection surfaces having respective first and second inclination angles and continuing thickness-wise of the reflector but different from each other, the first and second inclination angles being respectively set to reflect light from the semiconductor light-emitting element toward the immediate upward at thickness-wise center regions of the first and second reflection surfaces of the reflector.
The output light from the light-emission center of the semiconductor light-emitting element is reflected by the first reflection surface. At this time, the light reflected at a center region of the first reflection surface travels toward the immediately upward with respect to the surface of the substrate. Similarly, the output light from the light emitting element is reflected by the second surface. The reflection light at a center region of the second reflection surface travels toward immediate upward with respect to the surface of the substrate. Accordingly, the reflection light in the same direction due to a plurality of reflection surface is collected together. This increases the quantity of reflection light travelling toward a center axis of the radiation surface and improves center brightness. Also, because reflection toward the immediate upward can be made at the respective center regions of the first and second reflection surfaces, even if there occur positional deviation upon mounting the semiconductor light emitting element on the substrate, reflection light toward the immediate upward is available in the upper or lower areas of the first reflection surface and/or the second reflection surface with respect to the center area thereof, thereby reducing the variation in center brightness.
Incidentally, in a preferred embodiment, the first reflection surface is formed at a thickness-wise lower side of the reflector and the second reflection surface is formed at a thickness-wise upper side, the second inclination angle being greater as compared to the first inclination angle. If the first inclination angle be set greater than the second inclination angle, no output light reaches the area of the second reflection surface close to the first reflection surface from the semiconductor light emitting element due to blockage by the first reflection surface. This reduces the quantity of the output light reflected by the second reflection surface. Contrary to this, by setting the second inclination angle greater than the first reflection angle, there will not occur such partial shield in the output light hence further improving light emission efficiency.
Incidentally, a shape of the aperture as viewed from above can be selected as an arbitrary form, such as a circular form, a rectangular form or an oval form.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.